SPRINGDALE  State health officials are trying to determine the cause of an illness that sickened more than 300 students at Hellstern Middle School in Springdale.

School officials postponed Friday classes after 316 students either stayed home sick or left school early on Thursday because of a stomach ailment. The school has about 900 students.

State epidemiologist Dirk Haselow told TheSpringdale Morning News that the symptoms include vomiting, nausea and diarrhea — signs of a norovirus. Haselow said that can’t be confirmed until testing of samples from the students is complete.

The norovirus affects a person’s stomach, intestines or both and the federal Centers for Disease Control says it is highly contagious.

The school was already scheduled to be closed Monday for Martin Luther King Jr. Day and is to reopen Tuesday.